auto reset IR switch with delay

Discussion in 'The Projects Forum' started by dport, Jun 18, 2009.

  1. dport

    Thread Starter New Member

    Jun 18, 2009
    Greetings fellow project enthusiasts,

    I've been trying to put together an IR switch circuit with a 555 timer whose output is high (non-pulsed) after a 10-60 second delay when the emitter beam is broken. When the beam detected, the output is low and the timer automatically resets itself so that when the beam is next broken the output would again be delayed before going high.

    The transition time is not critical here. We can assume at least 1 second between beam on/off/on states.

    I've attached a design that seems to work. The LED is on after a suitable delay set by C and R but I'm nervous about shorting THR across the phototransitor. Will this be stable if the beam is unbroken for a long period?

    Any help is most appreciated!
    Last edited: Jun 21, 2009